Motor drive control device, motor unit, and motor drive control method

Abstract

To suppress an increase in power consumption of a motor.SOLUTION: A control circuit 1 includes: a commutation mode setting part 11 that selects a first commutation mode that performs commutation of a coil 41 on the basis of a detection result of a zero cross of an inverse voltage of the coil 41 of a motor 4 or a second commutation mode that performs the commutation of the coil 41 in accordance with a target power conduction time, and sets the mode as a commutation mode; a drive control signal generation part 12 that generates a drive control signal Sd on the basis of the set commutation mode; a current limit value setting part 14 that sets a current limit value; and a current limit part 16 that instructs the drive control signal generation part 12 to stop an excitation of the coil 41 in the case where a current flowing through the coil 41 reaches a current limit value. The current limit value setting part 14 sets the current limit value to an upper limit value Ith1 in a period when the commutation mode is in the first commutation mode, and sets the curent limit value to a lower limit value Ith2 smaller than the upper limit value Ith1 at least a part in a period in the second commutation mode.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a motor drive control device, a motor unit, and a motor drive control method, and relates to a motor drive control device for driving, for example, a stepping motor. [Background technology]

[0002] Conventionally, motor drive control devices have been known that have a current limiting function that limits the current flowing through a motor coil (hereinafter also referred to as "coil current") so that it does not exceed a preset value (hereinafter also referred to as "current limit value") (see, for example, Patent Document 1). Also known is a motor drive control device that detects the zero crossing of the back electromotive force of a motor coil and performs commutation of the coil (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-207607 A [Patent Document 2] JP 2018-38213 A Summary of the Invention [Problem to be solved by the invention]

[0004] Prior to filing this application, the present inventors investigated a new motor drive control technology. Specifically, the inventors investigated a motor drive control technology that controls a motor so that the coil current of the motor does not exceed a current limit value, performs coil commutation based on zero crossings of the back electromotive force of the coil when the motor rotation speed is lower than a threshold, and performs coil commutation according to a preset commutation time when the motor rotation speed is equal to or higher than the threshold. However, the present inventors discovered that the above motor drive control technology has the following problems.

[0005] That is, with the motor drive control technology, as the load on the motor becomes lighter, the motor's rotation speed increases, and when the motor's rotation speed reaches a threshold, the motor is controlled so that the rotation speed is equal to or less than the threshold. Meanwhile, the coil current can increase up to the current limit value regardless of the motor's rotation speed. Therefore, when the motor's load becomes lighter, more coil current than necessary may flow, resulting in higher power consumption by the motor.

[0006] The present invention has been made in view of the above-mentioned problems, and has an object to suppress an increase in the power consumption of a motor. [Means for solving the problem]

[0007] A motor drive control device according to a representative embodiment of the present invention includes a control circuit that generates drive control signals for controlling drive of a motor, and a drive circuit that drives a coil of the motor based on the drive control signals. The control circuit has a commutation mode setting unit that selects, based on the rotational speed of the motor, a first commutation mode in which the coil is commutated based on detection results of zero crossings of a back electromotive force of the coil, or a second commutation mode in which the coil is commutated in accordance with a target current flow time, and sets the selected mode as the commutation mode. The control circuit also has a drive control signal generation unit that generates the drive control signal based on the commutation mode set by the commutation mode setting unit. A current limit value setting unit sets a current limit value that serves as a reference for limiting a current flowing through the coil. A current limit unit that instructs the drive control signal generation unit to stop excitation of the coil when the current flowing through the coil reaches the current limit value. The current limit value setting unit sets the current limit value to a first value during a period in which the commutation mode is the first commutation mode, and sets the current limit value to a second value that is smaller than the first value during at least a portion of a period in which the second commutation mode is in effect. [Effects of the Invention]

[0008] According to the motor drive control device of the present invention, it is possible to suppress an increase in the power consumption of the motor. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a block diagram showing the configuration of a motor unit according to the embodiment. [Figure 2] FIG. 2 is a diagram schematically illustrating the configuration of a motor. [Figure 3] FIG. 2 is a diagram illustrating a configuration of a control circuit in the motor drive control device according to the embodiment. [Figure 4] 4 is a timing chart showing an example of the operation of a motor and a motor drive control device in response to a change in load. [Figure 5] 5 is a timing chart showing an example of a change in coil current when a motor is driven by a motor drive control device according to an embodiment. [Figure 6] 10 is a flowchart showing a flow of a process for switching a current limit value according to an embodiment. [Figure 7] 10 is a flowchart showing the flow of a process (step S1) for setting a commutation mode. DETAILED DESCRIPTION OF THE INVENTION

[0010] 1. Overview of the embodiment First, a typical embodiment of the invention disclosed in this application will be outlined. In the following description, for example, reference numerals in the drawings corresponding to components of the invention are written in parentheses.

[0011] [1] A motor drive control device (3) according to a representative embodiment of the present invention includes a control circuit (1) that generates a drive control signal (Sd) for controlling the drive of a motor (4), and a drive circuit (2) that drives coils (41A, 41B) of the motor based on the drive control signal, wherein the control circuit includes a commutation mode setting unit (11) that selects, based on the rotation speed of the motor, a first commutation mode in which commutation of the coils is performed based on a detection result of zero crossing of a back electromotive force of the coils, or a second commutation mode in which commutation of the coils is performed in accordance with a target current application time, and sets the selected mode as the commutation mode; The inverter includes a drive control signal generating unit (12) that generates the drive control signal based on the above-mentioned method, a current limit value setting unit (14) that sets a current limit value that serves as a reference for limiting the current flowing through the coil, and a current limiting unit (16) that instructs the drive control signal generating unit to stop exciting the coil when the current flowing through the coil reaches the current limit value, wherein the current limit value setting unit sets the current limit value to a first value (Ith1) during a period in which the commutation mode is the first commutation mode, and sets the current limit value to a second value (Ith2) that is smaller than the first value during at least a portion of a period in which the commutation mode is the second commutation mode.

[0012] [2] In the motor drive control device described in [1] above, the commutation mode setting unit may set the commutation mode to the first commutation mode when the rotation speed of the motor has not reached a first threshold (Sth1), set the commutation mode to the second commutation mode when the rotation speed of the motor has reached the first threshold, and set the commutation mode to the first commutation mode when the rotation speed of the motor has dropped to a second threshold (Sth2) that is smaller than the first threshold while the commutation mode is the second commutation mode.

[0013] [3] In the motor drive control device described in [1] or [2] above, the current limit value setting unit may change the current limit value in a stepwise manner from the first value to the second value when the zero crossing of the back electromotive force cannot be detected after the commutation mode is switched from the first commutation mode to the second commutation mode.

[0014] [4] In the motor drive control device described in any one of [1] to [3] above, the current limit value setting unit may change the current limit value in a stepwise manner from the second value to the first value when a zero crossing of the back electromotive force is detected when the commutation mode is the second commutation mode.

[0015] [5] In the motor drive control device described in any of [1] to [4] above, the rate of change of the current limit value with respect to the time when the current limit value switches from the second value to the first value may be greater than the rate of change of the current limit value with respect to the time when the current limit value switches from the first value to the second value.

[0016] [6] In the motor drive control device described in any one of [1] to [5] above, the current limit value setting unit may periodically determine whether or not a zero cross of the back electromotive force has been detected, and may increase the current limit value if a zero cross of the back electromotive force has been detected, and may decrease the current limit value if a zero cross of the back electromotive force has not been detected.

[0017] [7] A motor unit (5) according to a representative embodiment of the present invention is characterized by comprising the motor (4) and the motor drive control device (3) described in any one of [1] to [6] above.

[0018] [8] A method according to a representative embodiment of the present invention is a motor drive control method for controlling the drive of a motor by a motor drive control device, comprising: a first step (S1) in which the motor drive control device sets, based on the rotation speed of the motor, a first commutation mode in which the motor coil is commutated based on a detection result of zero crossing of a back electromotive force of the coil, or a second commutation mode in which the coil is commutated according to a target current application time; a second step (S2) in which the motor drive control device generates a drive control signal for controlling the drive of the motor; and a second step (S3) in which the motor drive control device limits a current flowing in the coil. a fourth step in which the motor drive control device generates the drive control signal for stopping excitation of the coil when the current flowing through the coil reaches the current limit value; the third step includes a fifth step (S4 to S7) in which the motor drive control device sets the current limit value to a first value during a period in which the commutation mode is the first commutation mode; and a sixth step (S5 to S9) in which the motor drive control device sets the current limit value to a second value smaller than the first value during at least a part of a period in which the motor is in the second commutation mode.

[0019] 2. Specific examples of embodiments Hereinafter, specific examples of embodiments of the present invention will be described with reference to the drawings. In the following description, components common to the embodiments will be designated by the same reference numerals, and repeated description will be omitted.

[0020] <Embodiment> FIG. 1 is a block diagram showing the configuration of a motor unit 5 according to an embodiment.

[0021] 1, the motor unit 5 includes a motor 4 and a motor drive control device 3 that drives the motor 4. The motor unit 5 is applicable to various devices that use a motor as a power source, such as an actuator that can be used in an HVAC (Heating, Ventilation, and Air-Conditioning) air conditioning unit for vehicle use, for example.

[0022] The motor 4 is, for example, a stepping motor. In this embodiment, the motor 4 is, for example, a two-phase stepping motor.

[0023] FIG. 2 is a diagram schematically illustrating the configuration of the motor 4. As shown in FIG.

[0024] As shown in Fig. 2, motor 4, which is a two-phase stepping motor, has A-phase coil 41A, B-phase coil 41B, and rotor 42. Coils 41A and 41B are wound around a stator yoke (not shown) and form a stator together with the stator yoke. In this embodiment, when coils 41A and 41B are not to be distinguished from each other, they may be simply referred to as "coil 41."

[0025] As shown in Fig. 2, the rotor 42 is provided with a multi-pole magnetized permanent magnet in which south poles 42S and north poles 42S are alternately arranged along the circumferential direction. Note that Fig. 2 shows an example in which the rotor 42 has two poles, but the number of poles of the rotor 42 is not particularly limited.

[0026] When a current flows through the A-phase coil 41A, the A-phase stator yoke is excited, and when a current flows through the B-phase coil 41B, the B-phase stator yoke is excited. The phases of the currents flowing through the coils 41A and 41B are periodically switched, causing the rotor 42 to rotate. An output shaft (not shown) is connected to the rotor 42, and the output shaft is driven by the rotational force of the rotor 42, thereby realizing, for example, the function as the actuator described above.

[0027] The motor drive control device 3 is a device for driving the motor 4. The motor drive control device 3 controls the rotation and stopping of the motor 4 by controlling the energization state of the coils 41A, 41B of each phase of the motor 4, for example, based on a drive command signal Sc from the higher-level device 6.

[0028] As shown in FIG. 1, the motor drive control device 3 includes a control circuit 1 and a drive circuit 2. The drive circuit 2 is a circuit that energizes the coils 41A and 41B of the motor 4 to drive the motor 4. The drive circuit 2 is a circuit that excites the coils 41A and 41B of the motor 4 based on a drive control signal Sd output from the control circuit 1, thereby rotating the rotor 42 of the motor 4.

[0029] The drive circuit 2 includes, for example, an inverter circuit 21A for exciting the A-phase coil 41A, an inverter circuit 21B for exciting the B-phase coil 41B, a current detection circuit 20A for detecting the current in the A-phase coil 41A, and a current detection circuit 20B for detecting the current in the B-phase coil 41B.

[0030] The inverter circuits 21A and 21B are configured, for example, by an H-bridge circuit configured of four switching elements (e.g., transistors). Hereinafter, the inverter circuit 21A will also be referred to as the "H-bridge circuit 21A," and the inverter circuit 21B will also be referred to as the "H-bridge circuit 21B." Furthermore, when there is no need to distinguish between the H-bridge circuit 21A and the H-bridge circuit 21B, they will simply be referred to as the "H-bridge circuit 21."

[0031] The H-bridge circuit 21A and the H-bridge circuit 21B have, for example, the same circuit configuration. Although not shown, the H-bridge circuit 21 has a plurality of switching elements (e.g., transistors) whose on / off states are controlled by the drive control signal Sd.

[0032] The drive circuit 2 may include a pre-drive circuit for driving the switching elements of the H-bridge circuits 21A and 21B based on the drive control signal Sd.

[0033] 2, the H-bridge circuit 21A is connected to a positive terminal AP of the coil 41A and a negative terminal AN of the coil 41A. The H-bridge circuit 21B is connected to a positive terminal BP of the coil 41B and a negative terminal BN of the coil 41B.

[0034] The H-bridge circuits 21A and 21B apply voltages to the terminals AP, AN, BP, and BN to energize the coils 41A and 41B. Specifically, the H-bridge circuit 21 selectively turns on and off the switching elements constituting the H-bridge circuit 21 in response to a drive control signal Sd supplied from the control circuit 1, thereby switching the coil 41 to be excited and switching the direction of current flow through the coil 41.

[0035] 2, during an "A-phase (+) excitation period" in which a current +Ia flows from terminal AP to terminal AN of the A-phase coil 41A, the H-bridge circuit 21A applies a voltage of "+Va" to terminal AP relative to terminal AN of the coil 41A. On the other hand, during an "A-phase (-) excitation period" in which a current -Ia flows from terminal AN to terminal AP of the A-phase coil 41A, the H-bridge circuit 21A applies a voltage of "-Va" to terminal AP relative to terminal AN of the coil 41A. During a "B-phase (+) excitation period" in which a current +Ib flows from terminal BP to terminal BN of the B-phase coil 41B, the H-bridge circuit 21B applies a voltage of "+Vb" to terminal BP relative to terminal BN of the coil 41B. During a "B-phase (-) excitation period" in which a current -Ib flows from terminal BN to terminal BP of B-phase coil 41B, H-bridge circuit 21B applies a voltage of "-Vb" to terminal BP relative to terminal BN of coil 41B.

[0036] The current detection circuit 20A is connected to the H-bridge circuit 21A, detects the current flowing through the coil 41A, and outputs a current detection signal Sia corresponding to the magnitude of the detected current. The current detection circuit 20B is connected to the H-bridge circuit 21B, detects the current flowing through the coil 41B, and outputs a current detection signal Sib corresponding to the magnitude of the detected current.

[0037] The current detection circuits 20A, 20B include, for example, shunt resistors. The shunt resistor is connected in series with the H-bridge circuit 21 between the power supply voltage and ground voltage of the H-bridge circuit 21, for example, for each H-bridge circuit 21, and outputs voltages generated across the shunt resistors as current detection signals Sia, Sib. Note that the current detection circuits 20A, 20B can employ various known circuit configurations capable of detecting the currents flowing through the coils 41A, 41B of the motor 4, and are not limited to the circuit configuration including the shunt resistors described above.

[0038] The control circuit 1 is a circuit that performs overall control of the motor drive control device 3. The control circuit 1 is a program processing device (e.g., a microcontroller) having a configuration in which a processor such as a CPU, various storage devices such as RAM and ROM, and peripheral circuits such as a timer (counter), an A / D conversion circuit, a D / A conversion circuit, and an input / output I / F circuit are connected to each other via a bus. In this embodiment, the control circuit 1 is packaged as, for example, an IC (integrated circuit), but is not limited to this. The control circuit 1 and the drive circuit 2 may also be packaged together.

[0039] The control circuit 1 has a function of controlling the driving of the motor 4 by generating a drive control signal Sd and providing it to the drive circuit 2, for example.

[0040] FIG. 3 is a diagram showing the configuration of the control circuit 1 in the motor drive control device 3 according to the embodiment.

[0041] As shown in FIG. 3, the control circuit 1 has, as functional units for realizing the above-mentioned functions, a commutation mode setting unit 11, a drive control signal generating unit 12, a memory unit 13, a current limit value setting unit 14, a current value acquiring unit 15, a current limiting unit 16, a zero-cross detecting unit 17, and a rotation speed calculating unit 18.

[0042] These functional units are realized, for example, by a program processing device (microcontroller) serving as the above-mentioned control circuit 1, in which a processor executes calculations using various parameters stored in a storage device in accordance with a program stored in the storage device, and controls peripheral circuits such as an A / D conversion circuit and a timer. Note that some or all of these functional units may be realized by dedicated circuits (hardware).

[0043] The storage unit 13 is a functional unit for storing various data necessary for motor drive control by the control circuit 1. For example, the storage unit 13 stores current limit value information 130, which includes an upper limit value (an example of a first value) Ith1, a lower limit value (an example of a second value) Ith2, a unit increment ΔIa, and a unit decrement ΔId of the current limit value, as will be described later.

[0044] The commutation mode setting unit 11 is a functional unit for setting a commutation mode that specifies the method of commutation of the motor 4.

[0045] The motor drive control device 3 according to this embodiment has at least two commutation modes. One is a first commutation mode in which the commutation of coils 41A, 41B is performed based on the detection result of the zero crossing of the back electromotive force of coils 41A, 41B, and the other is a second commutation mode in which the commutation of coil 41 is performed in accordance with a target current conduction time. Here, the target current conduction time is a target value for the length of a period during which one current conduction pattern (excited state of coil 41) is continued.

[0046] For example, the commutation mode setting unit 11 acquires a drive command signal Sc for the motor 4 input from outside the motor drive control device 3 (for example, from the higher-level device 6). The drive command signal Sc includes, for example, information specifying the rotational position of the motor 4 and information instructing the motor 4 to stop rotating. The drive command signal Sc is, for example, a PWM signal. For example, the commutation mode setting unit 11 analyzes the drive command signal Sc to acquire information on a target rotational position of the motor 4 (target rotational position), sets the commutation mode to the first commutation mode or the second commutation mode, and then instructs the drive control signal generating unit 12 to drive the motor 4. Note that the method of setting the commutation mode by the commutation mode setting unit 11 will be described in detail later.

[0047] The zero-cross detector 17 is a functional unit that monitors the voltages of the coils 41A and 41B and detects the zero-cross of the back electromotive force generated in the coils 41A and 41B. Here, the zero-cross of the back electromotive force refers to a state in which the back electromotive force generated across both ends of the unexcited coil 41 switches from positive to negative or from negative to positive.

[0048] The zero-cross detection unit 17 monitors the voltage between terminals AP and AN as the voltage of coil 41A, and monitors the voltage between terminals BP and BN as the voltage of coil 41B, and when it detects a zero-cross of the back electromotive force of coils 41A and 41B, it outputs a zero-cross detection signal Sz indicating that a zero-cross has been detected.

[0049] The rotation speed calculation unit 18 is a functional unit that calculates the rotation speed of the motor 4. When zero crossings of the back electromotive force of the coil 41 are detected periodically, the rotation speed calculation unit 18 calculates the rotation speed of the motor 4 based on the zero crossing detection signal Sz output from the zero crossing detection unit 17. For example, in the first commutation mode, the rotation speed calculation unit 18 calculates the rotation speed of the motor 4 based on the period at which the zero crossing detection signal Sz is output. On the other hand, when no back electromotive force is detected in the second commutation mode, the rotation speed calculation unit 18 calculates the rotation speed of the motor 4 based on, for example, a target current application time that is set in advance in the second commutation mode. The rotation speed calculation unit 18 generates an output signal So that includes information about the calculated rotation speed. The output signal So is output, for example, to an external device (e.g., the higher-level device 6) of the motor drive control device 3 and input to the commutation mode setting unit 11.

[0050] The drive control signal generation unit 12 generates the drive control signal Sd based on the commutation mode set by the commutation mode setting unit 11. The drive control signal Sd is a signal for controlling the on / off of each switching element of the H-bridge circuits 21A, 21B, and is, for example, a PWM signal.

[0051] The drive control signal generator 12 generates and outputs a drive control signal Sd to excite the A-phase coil 41A and the B-phase coil 41B at a predetermined timing based on a predetermined excitation method in order to move the rotor 42 to a target rotation position or a target standby position. Here, the predetermined excitation method may be any excitation method that allows detection of the back electromotive force of the coil 41, such as a well-known one-phase excitation method or one-two phase excitation method.

[0052] When generating the drive control signal Sd using the one-phase excitation method, the drive control signal generating unit 12 generates and outputs the drive control signal Sd so that the energization states of the A-phase and B-phase coils 41A and 41B are switched in the order of, for example, "A-phase (+) excitation period", "B-phase (+) excitation period", "A-phase (-) excitation period", and "B-phase (-) excitation period".

[0053] At this time, switching of each excitation period, that is, commutation of the coils 41A and 41B, is performed in accordance with the commutation mode set by the commutation mode setting unit 11. Specifically, when the first commutation mode is designated as the commutation mode, the drive control signal generation unit 12 commutates the coils 41A, 41B every time the zero-cross detection unit 17 detects a zero-cross of the back electromotive force. As in the above example, when the motor 4 is driven by the one-phase excitation method, for example, when the zero-cross detection unit 17 outputs the zero-cross detection signal Sz in the "A-phase (+) excitation period," the drive control signal generation unit 12 switches from the "A-phase (+) excitation period" to the "B-phase (+) excitation period."

[0054] Furthermore, when the second commutation mode is designated as the commutation mode, the drive control signal generating unit 12 performs commutation of the coils 41A and 41B based on the target current application time.

[0055] For example, the drive control signal generating unit 12 has a timer (counter) and starts measuring time when the "A phase (+) excitation period" starts, and when the measured time reaches the target current application time, switches from the "A phase (+) excitation period" to the "B phase (+) excitation period."

[0056] Here, the information on the target current-flow time may be stored in advance in drive control signal generating unit 12 or storage unit 13, or may be calculated by drive control signal generating unit 12. For example, information on the target rotation speed of motor 4 and information on the conduction angle that indicates the magnitude of the electrical angle at which current is continuously applied in one direction to the coil of one phase according to the excitation method may be stored in advance in storage unit 13, and drive control signal generating unit 12 may calculate the target current-flow time based on the information on the target rotation speed and the information on the conduction angle read from storage unit 13.

[0057] Note that, when a zero cross of the back electromotive force is detected in the second commutation mode, the drive control signal generating unit 12 may commutate the coils 41A, 41B in response to the detection of the zero cross of the back electromotive force (input of the zero cross detection signal Sz), as in the first commutation mode. That is, when a zero cross of the back electromotive force is not detected in the second commutation mode, the drive control signal generating unit 12 may commutate the coils 41A, 41B based on the target current application time, and when a zero cross of the back electromotive force is detected in the second commutation mode, the drive control signal generating unit 12 may commutate the coils 41A, 41B in response to the detection of the zero cross of the back electromotive force regardless of the target current application time, even in the second commutation mode.

[0058] The current value acquiring unit 15 is a functional unit that acquires the values ​​of the currents flowing through the coils 41A and 41B of each phase of the motor 4. The current detection signals Sia and Sib output from the current detection circuits 20A and 20B of the drive circuit 2 are input to the current value acquiring unit 15. The current value acquiring unit 15 includes, for example, an A / D conversion circuit, and converts the voltage as the current detection signal Sia into a digital value using the A / D conversion circuit, and outputs the digital value as the current value of the A-phase coil 41A. Similarly, the current value acquiring unit 15 converts the voltage as the current detection signal Sib into a digital value using, for example, the A / D conversion circuit, and outputs the digital value as the current value of the B-phase coil 41B.

[0059] The current limit value setting unit 14 is a functional unit for setting a current limit value. The current limit value is a reference value for limiting the current flowing through the coil 41 of the motor 4, in other words, a value that determines the upper limit of the current through the coil 41.

[0060] The current limit value setting unit 14 sets the current limit value based on the information on the commutation mode set by the commutation mode setting unit 11, the zero-cross detection signal Sz output from the zero-cross detection unit 17, and the current limit value information 130 stored in the storage unit 13. The method for setting the current limit value will be described in detail later.

[0061] The current limiting unit 16 is a functional unit that monitors the current flowing through the coil 41 of the motor 4 and controls the current so that it does not exceed a current limit value. The current monitoring by the current limiting unit 16 is performed for each phase of the motor 4. For example, during the "A-phase (+) excitation period" and "A-phase (-) excitation period" in which the A-phase coil 41A is excited, the current (current detection signal Sia) of the A-phase coil 41A is monitored, and during the "B-phase (+) excitation period" and "B-phase (-) excitation period" in which the B-phase coil 41B is excited, the current (current detection signal Sib) of the B-phase coil 41B is monitored.

[0062] When the current flowing through the coil 41 reaches a current limit value, the current limiting unit 16 instructs the drive control signal generating unit 12 to stop the excitation of the coil 41. For example, during the period when the A-phase coil 41A is excited, the current limiting unit 16 compares the current value (absolute value) of the coil 41A output from the current value acquiring unit 15 with the current limit value (absolute value) set by the current limit value setting unit 14, and when the current value of the coil 41A becomes equal to or greater than the current limit value, the current limiting unit 16 outputs a signal for a predetermined period instructing the excitation of the coil 41A to be stopped, i.e., to turn off each switching element of the H-bridge circuit 21A by the drive control signal Sd. The current limiting unit 16 also limits the current of the B-phase coil 41B during the period when the B-phase coil 41B is excited using a similar method.

[0063] The drive control signal generation unit 12 generates a drive control signal Sd to stop the excitation of the coil 41 while the current limiting unit 16 outputs a signal instructing the coil 41 to stop excitation. For example, if the current limiting unit 16 outputs a signal instructing the coil 41A to stop excitation during the "phase A (+) excitation period," the drive control signal generation unit 12 generates a drive control signal Sd to turn off each switching element in the phase A H-bridge circuit 21A. This stops the power supply to the phase A coil 41A, so the current in the phase A coil 41A decreases and is limited so as not to exceed the current limit value. The current in the phase B coil 41B is also limited in a similar manner.

[0064] Here, a method for setting the commutation mode will be described.

[0065] The commutation mode setting unit 11 selects the first commutation mode or the second commutation mode based on the rotation speed of the motor 4, and sets it as the commutation mode. For example, when the load on the motor 4 is heavy and the rotation speed of the motor 4 is relatively slow, it is easy to detect the zero crossing of the back electromotive force of the coil 41. Therefore, when the rotation speed of the motor 4 has not reached the first threshold value Sth1, the commutation mode setting unit 11 sets the commutation mode to the first commutation mode.

[0066] By setting the commutation mode to the first commutation mode, commutation of the coil 41 is performed in response to detection of the zero crossing of the back electromotive force, making it possible to rotate the motor 4 at an appropriate rotation speed and torque that follows the magnitude of the load.

[0067] On the other hand, when commutation of the coil 41 is performed in response to detection of zero crossings of the back electromotive force in the first commutation mode, the lighter the load on the motor 4, the higher the rotation speed of the motor 4 becomes, making it more difficult to detect zero crossings of the back electromotive force. Therefore, when the rotation speed of the motor 4 reaches the first threshold value Sth1, the commutation mode setting unit 11 sets the commutation mode to the second commutation mode.

[0068] By setting the commutation mode to the second commutation mode, the coil 41 is commutated in accordance with the target current-carrying time, which makes it possible to reliably rotate the motor 4 while avoiding loss of synchronism of the motor 4. At this time, the motor 4 rotates at a rotation speed in accordance with the target current-carrying time, thereby suppressing an increase in rotation speed.

[0069] As described above, when a zero crossing of the back electromotive force is detected in the second commutation mode, the coil 41 may be commutated in response to the detection of the zero crossing of the back electromotive force, as in the first commutation mode. In this case, the motor 4 rotates at a rotation speed according to the magnitude of the load.

[0070] Furthermore, when the rotation speed of the motor 4 drops to a second threshold value Sth2 while the commutation mode is the second commutation mode, the commutation mode setting unit 11 sets the commutation mode to the first commutation mode. Here, the second threshold value Sth2 is a value different from the first threshold value Sth1, and for example, the second threshold value Sth2<the first threshold value Sth1.

[0071] According to this, for example, when the load on the motor 4 starts to increase and the rotation speed decreases, the mode automatically returns from the second commutation mode to the first commutation mode, making it possible to drive the motor 4 at an appropriate rotation speed and torque according to the load. Also, by setting the second threshold value Sth2 and the first threshold value Sth1 for the threshold value of the rotation speed of the motor 4 to different values, it is possible to prevent the commutation mode from being frequently switched due to fluctuations in the rotation speed (load) of the motor 4.

[0072] Next, a method for setting the current limit value will be described.

[0073] As described above, when the load on the motor 4 becomes light and the motor 4 is rotating in the second commutation mode, the coil current may rise to the current limit value regardless of the rotation speed of the motor 4, causing more coil current than necessary to flow and resulting in higher power consumption. Therefore, the motor drive control device 3 according to this embodiment has a function for varying the current limit value.

[0074] Specifically, the current limit value setting unit 14 sets the current limit value to a first value, that is, an upper limit value Ith1, during a period in which the commutation mode is the first commutation mode, and sets the current limit value to a second value, that is, a lower limit value Ith2 (<upper limit value Ith1), which is smaller than the first value, during at least a portion of a period in which the second commutation mode is the second commutation mode.

[0075] For example, the current limit value setting unit 14 periodically determines whether or not a zero cross of the back electromotive force has been detected, and increases the current limit value when a zero cross of the back electromotive force has been detected, and decreases the current limit value when a zero cross of the back electromotive force has not been detected. The process of switching the current limit value will be described in detail below.

[0076] FIG. 4 is a timing chart showing an example of the operation of the motor 4 and the motor drive control device 3 in response to a change in the load.

[0077] In Fig. 4, the horizontal axis represents time t. Also, in Fig. 4, from the top to the bottom of the page, the load size, the rotation speed of motor 4, the current limit value, the commutation mode, and the zero-cross detection state of the back electromotive force are shown, respectively.

[0078] For example, as shown in FIG. 4, at time t0, the rotation speed of the motor 4 has not reached the first threshold value Sth1. Therefore, the commutation mode setting unit 11 sets the commutation mode to the first commutation mode. Furthermore, the current limit value setting unit 14 sets the current limit value to the upper limit value Ith1 as a first value. As a result, the motor 4 is controlled so that the coil current does not exceed the upper limit value Ith1 while rotating at a rotation speed according to the load. Note that information about the upper limit value Ith1 is stored in the storage unit 13 as, for example, current limit value information 130, and the current limit value setting unit 14 reads out and uses this information from the storage unit 13.

[0079] After time t0, motor 4 is similarly driven and controlled in the first commutation mode, and the rotational speed of motor 4 increases as the load decreases. Then, at time t1, when the rotational speed of motor 4 reaches first threshold value Sth1, commutation mode setting unit 11 switches the commutation mode from the first commutation mode to the second commutation mode. As a result, drive control signal generation unit 12 commutates coil 41 based on a preset target current-carrying time, and motor 4 rotates at a rotational speed corresponding to the target current-carrying time.

[0080] When the current limit value setting unit 14 determines that the zero crossing of the back electromotive force can no longer be detected after the commutation mode has been switched from the first commutation mode to the second commutation mode, the current limit value setting unit 14 starts a process of switching the current limit value from the upper limit value Ith1 as a first value to the lower limit value Ith2 as a second value.

[0081] For example, as shown in Fig. 4, after the commutation mode is switched from the first commutation mode to the second commutation mode at time t1, it is assumed that the zero crossing of the back electromotive force cannot be detected at time t2. At this time, the current limit value setting unit 14 changes (reduces) the current limit value in stages from the upper limit value Ith1 to the lower limit value Ith2.

[0082] For example, the current limit value setting unit 14 changes the current limit value in stages in synchronization with the determination of whether or not a zero cross of the back electromotive force has been detected. Specifically, the current limit value setting unit 14 periodically determines whether or not a zero cross of the back electromotive force has been detected, and reduces the current limit value by a unit amount according to the determination result.

[0083] For example, the current limit value setting unit 14 determines whether or not the zero-cross detection signal Sz has been output during a certain period of time (whether or not a zero cross has been detected), and if the zero-cross detection signal Sz has not been output during that certain period of time, reduces the current limit value by the unit decrease amount ΔId. Note that information on the lower limit value Ith1 and information on the unit decrease amount ΔId are stored in the storage unit 13 as, for example, current limit value information 130, and the current limit value setting unit 14 reads out this information from the storage unit 13 and uses it.

[0084] After time t2, the current limit value setting unit 14 cannot detect a zero crossing of the back electromotive force, and so reduces the current limit value by a unit decrement ΔId at regular intervals. Then, at time t3, the current limit value reaches the lower limit value Ith2. At this time, the current limit value setting unit 14 stops the process of reducing the current limit value. As a result, after time t3, the motor 4 rotates at a rotation speed according to the target energization time, while controlling the coil current so that it does not exceed the lower limit value Ith2.

[0085] When the commutation mode is the second commutation mode, if a zero crossing of the back electromotive force is detected, the current limit value setting unit 14 starts a process of switching the current limit value from the lower limit value Ith2 as the second value to the upper limit value Ith1 as the first value.

[0086] For example, as shown in Fig. 4, assume that the load starts to increase after time t3, and zero crossings of the back electromotive force begin to be detected at time t4. At this time, the current limit value setting unit 14 gradually changes (increases) the current limit value from a lower limit value Ith2 to an upper limit value Ith1. Specifically, the current limit value setting unit 14 periodically determines whether or not a zero crossing of the back electromotive force has been detected, and increases the current limit value by a unit amount depending on the determination result.

[0087] For example, the current limit value setting unit 14 determines whether or not the zero-cross detection signal Sz has been output (whether or not a zero cross has been detected) within a certain period of time, and increases the current limit value by a unit increment ΔIa each time the zero-cross detection signal Sz is output. Note that information about the unit increment ΔIa is stored in the storage unit 13 as current limit value information 130, for example, and the current limit value setting unit 14 reads out the information from the storage unit 13 and uses it.

[0088] After time t4, the current limit value setting unit 14 increases the current limit value by a unit increment ΔIa each time a zero crossing of the back electromotive force is detected, and when the current limit value reaches the upper limit value Ith1 at time t5, the current limit value setting unit 14 stops the process of increasing the current limit value.

[0089] After time t4, the commutation mode is the second commutation mode, but the zero crossing of the back electromotive force is detected. Therefore, the drive control signal generator 12 may perform commutation of the coil 41 in response to the detection of the zero crossing of the back electromotive force, regardless of the set commutation mode (second commutation mode). As a result, after time t4, the rotation speed of the motor 4 decreases as the load increases.

[0090] Then, at time t6, the rotation speed of the motor 4 drops to the second threshold value Sth2. At this time, the commutation mode setting unit 11 switches the commutation mode from the second commutation mode to the first commutation mode. As a result, the motor 4 is again controlled so that the coil current does not exceed the upper limit value Ith1 while rotating at a rotation speed according to the load.

[0091] At this time, since the zero crossing of the back electromotive force is detected periodically in accordance with the rotation speed of the motor 4, the current limit value setting unit 14 maintains the current limit value at the upper limit value Ith1 as the first value.

[0092] 4, the rate (absolute value) of change in the current limit value relative to time when the current limit value switches from the lower limit value (second value) Ith2 to the upper limit value (first value) Ith1 may be different from the rate (absolute value) of change in the current limit value relative to time when the current limit value switches from the upper limit value Ith1 to the lower limit value Ith2. For example, the unit increase amount ΔIa and the unit decrease amount ΔId may be different values.

[0093] Preferably, as shown in Fig. 4, the rate (absolute value) of change in the current limit value with respect to time when the current limit value switches from the lower limit value Ith2 to the upper limit value Ith1 is greater than the rate (absolute value) of change in the current limit value with respect to time when the current limit value switches from the upper limit value Ith1 to the lower limit value Ith2. For example, the unit increase amount ΔIa is greater than the unit decrease amount ΔId.

[0094] 4, it is preferable that the time taken for the current limit value to reach the upper limit value Ith1 from the lower limit value Ith2 (the period from time t4 to time t5) be shorter than the time taken for the current limit value to reach the lower limit value Ith2 from the upper limit value Ith1 (the period from time t2 to time t3). This is because the load increases when the current limit value switches from the lower limit value Ith2 to the upper limit value Ith1, and therefore, by shortening the time taken for the current limit value to reach the upper limit value Ith1 from the lower limit value Ith2 and quickly increasing the current limit value as described above, it is possible to avoid a shortage of rotational torque due to an increase in load.

[0095] FIG. 5 is a timing chart showing an example of changes in coil current when the motor 4 is driven by the motor drive control device 3 according to the embodiment.

[0096] In Fig. 5, the horizontal axis represents time t, and the vertical axis represents current. Fig. 5 shows the temporal changes in the current in the A-phase coil 41A and the B-phase coil 41B when the current limit value is reduced from the upper limit value Ith1 to the lower limit value Ith2 in the case where the motor 4 is driven using the one-phase excitation method. For example, times t0 to t3 in Fig. 5 correspond to times t0 to t3 in the timing chart of Fig. 4.

[0097] In Figure 5, for convenience of illustration, the current in the A-phase coil 41A (A-phase current) and the current in the B-phase coil 41B (B-phase current) are shown by the same solid line, and an explanation is provided near the solid line to identify the coil 41 of the phase through which the current flows.

[0098] 5, for example, during the period from time t0 to time t1 during which the motor 4 is driven and controlled in the first commutation mode, the drive control signal generator 12 switches the coil 41 to be excited in response to the detection of a zero-crossing of the back electromotive force. During the excitation period of each phase, if the current through the coil 41 is smaller than the absolute value |Ith1| of the upper limit, the drive control signal generator 12 continues to excite the coil 41 in one direction. When the current through the coil 41 reaches the absolute value |Ith1| of the upper limit, the drive control signal generator 12 stops exciting the coil 41 in response to an instruction from the current limiter 16, and then resumes exciting the coil 41 after a certain period of time has elapsed. This process is repeated.

[0099] Thereafter, the load on the motor 4 gradually decreases, and at time t1, when the rotation speed of the motor 4 reaches the first threshold value Sth1, the commutation mode switches from the first commutation mode to the second commutation mode. After the commutation mode switches to the second commutation mode, at time t2, when the zero crossing of the back electromotive force of the coil 41 is no longer detected, the process of switching the current limit value from the upper limit value Ith1 to the lower limit value Ith2 starts.

[0100] After time t2, the current limit value decreases stepwise from the upper limit value Ith1 and reaches the lower limit value Ith2 at time t3. During the period from time t2 to time t3, the current limit value changes stepwise as described above, and therefore the current in the coil 41 also changes stepwise, as shown in FIG.

[0101] Although not shown in the figure, when the commutation mode transitions from the second commutation mode to the first commutation mode, the current limit value changes from the lower limit value Ith2 to the upper limit value Ith1, and the current in coil 41 also changes in stages.

[0102] Next, the flow of the current limit value switching process will be described.

[0103] FIG. 6 is a flowchart showing the flow of the current limit value switching process according to the embodiment.

[0104] For example, first, the control circuit 1 sets the commutation mode (step S1). The process of setting the commutation mode in step S1 is executed according to the flow shown in FIG.

[0105] FIG. 7 is a flowchart showing the flow of the commutation mode setting process (step S1).

[0106] In the process of setting the commutation mode, first, the commutation mode setting unit 11 determines whether the current commutation mode is the first commutation mode and whether the rotation speed of the motor 4 has reached the first threshold value Sth1 (step S11).

[0107] If the commutation mode is the first commutation mode and the rotation speed of the motor 4 has reached the first threshold value Sth1 (step S11: YES), the commutation mode setting unit 11 sets the commutation mode to the second commutation mode (step S14).

[0108] On the other hand, in step S11, if the commutation mode is not the first commutation mode and / or the rotation speed of the motor 4 has not reached the first threshold value Sth1 (step S11: NO), the commutation mode setting unit 11 determines whether the commutation mode at that time is the second commutation mode and whether the rotation speed of the motor 4 has decreased below the second threshold value Sth2 (step S12).

[0109] If the commutation mode is the second commutation mode and the rotation speed of the motor 4 is equal to or lower than the second threshold value Sth2 (step S12: YES), the commutation mode setting unit 11 sets the commutation mode to the first commutation mode (step S14).

[0110] On the other hand, in step S12, if the commutation mode is not the second commutation mode and / or if the rotation speed of the motor 4 has not decreased below the second threshold value Sth2 (step S12: NO), the commutation mode setting unit 11 does not change the commutation mode.

[0111] After the above-described process of setting the commutation mode (step S1), as shown in FIG. 6, the control circuit 1 determines whether the commutation mode is the second commutation mode (step S2).

[0112] If the commutation mode is not the second commutation mode, that is, if the commutation mode is the first commutation mode (step S2: NO), the control circuit 1 increases the current limit value (step S4). Specifically, the current limit value setting unit 14 calculates a value by adding the unit increase amount ΔIa to the current limit value at that time.

[0113] Next, the current limit value setting unit 14 determines whether the value calculated in step S4 is greater than the upper limit value Ith1 (step S6). If the value calculated in step S4 is not greater than the upper limit value Ith1 (step S6: NO), the current limit value setting unit 14 sets the value calculated in step S4 as the current limit value, and the control circuit 1 repeats the processes of steps S1 to S9.

[0114] On the other hand, in step S6, if the value calculated in step S4 is greater than the upper limit value Ith1 (step S6: YES), the current limit value setting unit 14 sets the upper limit value Ith1 as the current limit value (step S7). Thereafter, the control circuit 1 repeatedly performs the processes of steps S1 to S9.

[0115] On the other hand, if the commutation mode is the second commutation mode in step S2 (step S2: YES), the control circuit 1 determines whether or not a zero cross of the back electromotive force is detected (step S3). If a zero cross of the back electromotive force is detected (step S3: YES), the control circuit 1 performs the processes of steps S4 to S7 described above.

[0116] If the zero crossing of the back electromotive force is not detected (step S3: NO), the control circuit 1 reduces the current limit value (step S5). Specifically, the current limit value setting unit 14 calculates a value by subtracting the unit decrease amount ΔId from the current current limit value at that time.

[0117] Next, the current limit value setting unit 14 determines whether the value calculated in step S5 is smaller than the lower limit value Ith2 (step S8). If the value calculated in step S5 is not smaller than the lower limit value Ith2 (is equal to or greater than the lower limit value Ith2) (step S8: NO), the current limit value setting unit 14 sets the value calculated in step S5 as the current limit value, and the control circuit 1 repeatedly performs the processes of steps S1 to S9.

[0118] On the other hand, in step S8, if the value calculated in step S5 is smaller than the lower limit value Ith2 (step S8: YES), the current limit value setting unit 14 sets the lower limit value Ith2 as the current limit value (step S9). Thereafter, the control circuit 1 repeatedly performs the processes of steps S1 to S9.

[0119] As described above, in the motor drive control device 3 according to this embodiment, the control circuit 1 sets the current limit value to a first value (upper limit value Ith1) during the period when the commutation mode is the first commutation mode, and sets the current limit value to a second value (lower limit value Ith2) that is smaller than the first value during at least a portion of the period when the commutation mode is the second commutation mode.

[0120] This makes it possible to prevent the current in the coil 41 from becoming unnecessarily large and the power consumption of the motor 4 from increasing, for example, when the load becomes lighter, the rotation speed of the motor 4 decreases, and the drive control of the motor 4 is being performed in the second commutation mode.

[0121] Furthermore, when the control circuit 1 is unable to detect the zero crossing of the back electromotive force after the commutation mode is switched from the first commutation mode to the second commutation mode, it changes (reduces) the current limit value in stages from a first value (upper limit value Ith1) to a second value (lower limit value Ith2).

[0122] This makes it possible to prevent the current in the coil 41 from dropping sharply and causing the operation of the motor 4 to become unstable when the commutation mode shifts from the first commutation mode to the second commutation mode.

[0123] Furthermore, when the commutation mode is the second commutation mode, if the control circuit 1 detects a zero crossing of the back electromotive force, it changes (increases) the current limit value in stages from a second value (lower limit value Ith2) to a first value (upper limit value Ith1).

[0124] This allows the coil current to be increased before the rotation speed of the motor 4 decreases due to an increase in load and the commutation mode completely shifts from the second commutation mode to the first commutation mode, thereby preventing the motor 4 from losing synchronism due to a shortage of coil current in the first commutation mode. Also, by increasing the current limit value in stages, it is possible to prevent the current in the coil 41 from increasing abruptly, causing the operation of the motor 4 to become unstable.

[0125] Furthermore, as mentioned above, it is preferable that the rate of change of the current limit value with respect to time when the current limit value switches from the second value (lower limit value Ith2) to the first value (upper limit value Ith1) is greater than the rate of change of the current limit value with respect to time when the current limit value switches from the first value (upper limit value Ith1) to the second value (lower limit value Ith2).

[0126] As a result, when the load is reduced, the increase in unnecessary coil current to the motor 4 can be more quickly suppressed, and when the load is increased, the coil current required to drive the motor 4 can be more quickly supplied, thereby achieving a good balance between reducing power consumption and ensuring stable operation of the motor 4.

[0127] In addition, the control circuit 1 may periodically determine whether or not a zero cross of the back electromotive force has been detected, and may increase the current limit value if a zero cross of the back electromotive force has been detected, and may decrease the current limit value if a zero cross of the back electromotive force has not been detected. According to this, the current limit value is adjusted in accordance with fluctuations in the load on the motor 4, so that more stable driving of the motor 4 can be achieved.

[0128] <<Extension of Embodiment>> The invention made by the inventor has been specifically described above based on an embodiment, but it goes without saying that the invention is not limited thereto and can be modified in various ways without departing from the spirit of the invention.

[0129] For example, the number of phases of the stepping motor serving as motor 4 in the above-described embodiments is not limited to two. Furthermore, motor 4 in the above-described embodiments is not limited to a stepping motor. For example, the motor may be a brushless DC motor.

[0130] In the above embodiment, the current limit value is changed stepwise in synchronization with the determination of whether or not a zero crossing of the back electromotive force has been detected. However, the present invention is not limited to this. For example, the current limit value may be changed stepwise per unit time. For example, when a zero crossing of the back electromotive force cannot be detected in the second commutation mode, the current limit value may be decreased stepwise from the upper limit value Ith1 to the lower limit value Ith2 per unit time, and when a zero crossing of the back electromotive force can be detected in the second commutation mode, the current limit value may be increased stepwise from the lower limit value Ith2 to the upper limit value Ith1 per unit time.

[0131] Furthermore, the above-described flowcharts are merely examples for explaining the operation, and are not intended to be limiting. That is, the steps shown in each diagram of the flowchart are specific examples, and the present invention is not limited to these flows. For example, the order of some processes may be changed, other processes may be inserted between processes, or some processes may be performed in parallel. [Explanation of symbols]

[0132] 1...control circuit, 2...drive circuit, 3...motor drive control device, 4...motor, 5...motor unit, 6...host device, 11...commutation mode setting unit, 12...drive control signal generation unit, 13...storage unit, 14...current limit value setting unit, 15...current value acquisition unit, 16...current limit unit, 17...zero cross detection unit, 18...rotation speed calculation unit, 20A, 20B...current detection circuit, 21, 21A, 21B...H-bridge circuit (inverter circuit), 42...rotor, 42S...South pole , 42N...North pole, 41, 41A, 41B...coil, 130...current limit value information, AP, AN, BP, BN...terminals of coils 41A, 41B, Ith1...upper limit value (an example of a first value), Ith2...lower limit value (an example of a second value), ΔIa...unit increase amount, ΔId...unit decrease amount, Sc...drive command signal, Sd...drive control signal, Sia, Sib...current detection signal, So...output signal, Sth1...first threshold, Sth2...second threshold, Sz...zero cross detection signal.

Claims

1. a control circuit that generates a drive control signal for controlling the drive of the motor; a drive circuit that drives a coil of the motor based on the drive control signal, The control circuit a commutation mode setting unit that selects, based on the rotation speed of the motor, a first commutation mode in which commutation of the coil is performed based on a detection result of zero crossing of a back electromotive force of the coil, or a second commutation mode in which commutation of the coil is performed in accordance with a target current application time, and sets the selected mode as the commutation mode; a drive control signal generation unit that generates the drive control signal based on the commutation mode set by the commutation mode setting unit; a current limit value setting unit that sets a current limit value that serves as a reference for limiting the current flowing through the coil; a current limiting unit that instructs the drive control signal generating unit to stop excitation of the coil when the current flowing through the coil reaches the current limit value, The current limit value setting unit sets the current limit value to a first value during a period in which the commutation mode is the first commutation mode, and sets the current limit value to a second value smaller than the first value during at least a portion of a period in which the commutation mode is the second commutation mode. Motor drive control device.

2. 2. The motor drive control device according to claim 1, The commutation mode setting unit sets the commutation mode to the first commutation mode when the rotation speed of the motor has not reached a first threshold, sets the commutation mode to the second commutation mode when the rotation speed of the motor has reached the first threshold, and sets the commutation mode to the first commutation mode when the rotation speed of the motor has decreased to a second threshold that is smaller than the first threshold while the commutation mode is the second commutation mode. Motor drive control device.

3. 3. The motor drive control device according to claim 2, The current limit value setting unit changes the current limit value stepwise from the first value to the second value when a zero cross of the back electromotive force cannot be detected after the commutation mode is switched from the first commutation mode to the second commutation mode. Motor drive control device.

4. 4. The motor drive control device according to claim 3, The current limit value setting unit changes the current limit value stepwise from the second value to the first value when a zero crossing of the back electromotive force is detected while the commutation mode is the second commutation mode. Motor drive control device.

5. 5. The motor drive control device according to claim 4, The rate of change of the current limit value with respect to time when the current limit value switches from the second value to the first value is greater than the rate of change of the current limit value with respect to time when the current limit value switches from the first value to the second value. Motor drive control device.

6. 3. The motor drive control device according to claim 2, The current limit value setting unit periodically determines whether or not a zero cross of the back electromotive voltage is detected, and increases the current limit value when a zero cross of the back electromotive voltage is detected, and decreases the current limit value when a zero cross of the back electromotive voltage is not detected. Motor drive control device.

7. the motor; A motor unit comprising: a motor drive control device according to any one of claims 1 to 6.

8. A motor drive control method for controlling the drive of a motor by a motor drive control device, comprising: a first step in which the motor drive control device sets, as a commutation mode, a first commutation mode in which commutation of the coils of the motor is performed based on a detection result of zero crossing of a back electromotive force of the coils of the motor, or a second commutation mode in which commutation of the coils is performed in accordance with a target current application time, based on a rotational speed of the motor; a second step in which the motor drive control device generates a drive control signal for controlling the drive of the motor; a third step in which the motor drive control device sets a current limit value that serves as a reference for limiting the current flowing through the coil; a fourth step in which the motor drive control device generates the drive control signal for stopping excitation of the coil when the current flowing through the coil reaches the current limit value; The third step is a fifth step in which the motor drive control device sets the current limit value to a first value during a period in which the commutation mode is the first commutation mode; and a sixth step of setting the current limit value to a second value less than the first value during at least a portion of the second commutation mode. Motor drive control method.

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